Control apparatus



July 3i', 1945.

J. B. McMAHoN CONTROL APPARATUS Filed April 14, 1945 riff* v Inventov"Jer/ome B. McMahon by Qa/daf W 4Z M Attornegs under Patented July 31,.1945

UNITED STATES PATENT OFFICE (Cl. 1st-4158) .14 Claims.

This invention relates to control apparatus and more particularly toapparatus responsive to fluctuations in a condition to produce a controlforce which may be utilized to return the condition to its normal value.

One oi' the objects of the invention is to provide control apparatuswhose operating range can'be easily and quickly adjusted.

Another object oi' the inventionls to provide control apparatus in whichadjustment ot the operating range does not ailect the zero or set point.

Still another objectof the invention is to provide control apparatus inwhich re-setting movement is opposed by a iluid spring. According to oneoi the features of the invention the spring may be adjusted by varyingthe eirective fluid volume.

The above and other objects and advantages of the invention will be morereadily apparent from the following description when read -in connection with the accompanying drawing, in which the single ligure is adiagrammatic view with `parts in 'section of one form oi! apparatusembodying the inventione Apparatusofthischaracterisnormallyemployed tocontrol the temperature, pressure, rate oi iluw. or some other similarcondition to maintain it at a substantially constant normal value. Theparticular apparatus illustrated may be employed to control any suchcondition and includes an element Il shown as a Bourdon tube responitysuch, for example, as a pressure operated valve to regulate thecondition.

In order to compensate or to re-set the control couple Vto prevent overcontrol and hunting, there is provided according to the presentinvention a pressure responsive means connected to the control couple tore-adjust it prior to bringing the condition back to its normal value.As shown. this means comprises a channel shaped frame 29 upon which ismounted a pair of doubled wall bellows 3| and 32 with their inner endsconnected to the frame in axial alignment. The outer ends of the bellowsare closed by plates 33 and are connected through a rod or link Il whichcarries a bracket Il connected Ato the link il. The space between thewalls ol the bellows 3l is connected without substantial restriction tothe chamber 21 through a pipe IB and the space between'the walls of thebellows 32 is connected to the chamber 21 through a pipe 31 which isvariably restricted by an ustable valve 38. The bellows are enclosed byhousings or casings 39 which form closed chambers around the bellowssive to the condition. The control element il moves a lever il which isconnected through a link I! to one end oi' a floating lever, i3. The

opposite end of the lever il is connected to a link i4 and its centerpoint is pivoted to a dapper II pivoted at one end on a fixed bracket Ilandv 'cooperating at itsother end with a nossle `|1v carried bythebracket i.. The nappe: and nozzle rorm a control couple forvarying-the pressure in ythe nolleas is well understood in the art Thenasale is supplied with fluid, such as air strictedorifice Il and thepressure between the oriilce and nozzle is conducted through a pipor Ilto an expansible bellows I2. g The bellows 22 forms a parto( apressurrelay mechanism and operates a double ended valve 23 controlling opposedports .2l Il in' a valve block. Fluid under prsure is supplied to theport 2l through s pipe Il whichmay communicate with the samepressuresourceas'the pipe il; Fluid pressure as produced by the pressure relayis conducted into a chamber 'l1 in the valve which may beconnectsdthroughapipe Il toccntrol instrumentalpressure, from a pipeV ilthrough a re-' respectively.

In operation the chambers in the housings 39 may be evacuated to anydesired extent or may be filled -with a gas at any desired pressure, the

pressures in both chambers being equal. Preferably, both chambers arepartially evacuated to such an extent that the pressure in'neither onewill rise above atmospheric during operation.

In operation of the mechanism as so far described, a change in thecondition to move the lever Il coimter-clockwise will cause the lever i8to pivot around the upper end o! the link il and will move the dapper Iltoward the nozzle i1.

This will increase the pressure back of the nozzle operating .the relayto increase'the pressure in pipe Il thereby to eiIect operation of thecontrol lnstrumentallty to bring the condition back to normal value. Atthe vsaine time, the increased pressin'e in pipe 2l will be tranmiittedthrough pipe Il to the bellows Il to expand it thereby raising thebracket 8B and link i4. At this time the lever' Il will move about itsleft end as a pivot toi-aise the ilapperl! to its original position andtorestorethepressureinthe nomic andrelay mechanism.

'At the saine time pressure will be transmitted through the pipe 11 pastvalve ll at a slower rate -intc the bellows 82 gradually to expand it.Id-

nally. the pressure in bellows Il and 3 2 will be equalized so that thecompensating force produced by bellows li will be cancelled and thedapper IIwill again be underthe solseontrol of this sensitive elementIt. I! the instrument is properly.

adjusted the condition will by thistime have returned to its normalvalue and the apparatus will remain stationary.

Expansion of the bellows in response to a variation in the controlpressure will be opposed by changes in volume of the space within thehousings 39, which space forms in eiiect a iluid spring. It will benoted that an upward movement of the bellows decreases the space in theupper chamber to increase the pressure therein and simultaneouslyincreases the space in the lower chamber to decrease the pressuretherein and that 'auch upward movementis opposed by the sum of these twoforces.

In order to vary the operating or throttling range oi' the apparatus,the effective volume of the two chambers forming the air spring may bevaried and if this variation is equal in both chambers the zero or setpoint of the apparatus will not be changed. In order to accomplish thisthere is provided according to the present invention a second pair oi'housings 4I connected respectively through passages 42 with the lowerparts of the housings 39. An expansible bellows 43 is secured to theframe 29 and projects into each of the housings 4i. Expansion of thebellows may be controlled by screws 44 of opposite hand connected to theends of the bellows rerespectively and threaded into the lends oi asleeve 45 which may be turned through a hand wheel 46. 'I'he spacewithin the housings 4I around the bellows is filled with a liquid andoperation oi the hand wheel will cause variable amounts of this liquidto be forced into the housings 39 to vary the eil'ective volumethereof.A

It will be noted that the bellows 43 are of the same lsize 'so thatoperation of the hand' wheel .will cause equal movement of each bellowsand consequently willdisplace equal amounts of liquid into the'housings39. Therefore, when the hand wheel is operated, the variation ofeffective volume inthe housings 39 will be the same so that the balanceofthe instrument will not be dis-- turbed and its-set point will remainconstant. However, since the effective volume is changed, the resistanceto motion oil'ered by the iluid spring will be altered to change theoperating or throttling range of the apparatus. In other words, when thevolume is smaller a given change oi' pressure will produce a smallerdegree of movement than-when the volume is larger.

While one embodiment of the invention has been shown and described, itwill be understood Vthat this is illustrative only and is not intendedsponsive to variations in a condition for produc,-y

ing a pressure proportional to a function of the.

condition, a pressure. responsive member responsive to said pressure tobe moved thereby and connected to said means to move it, means forming aclosed chamber containing s. compressible iiuid whose volume is variedby movement oi lsaid member-,- and means to force a variable connectedto said means to move it, housing means inclosing one side o! saidmember and containing a compressible fluid, and adjustable means to varythe eilective volume of the housing me'ans.

3. Control apparatus comprising means responsive to variations in acondition for producing a pressure proportional to a function of thecondition, a pressure responsive member responsive to said pressure tobe movedl thereby and connected to said means to move it.v housing meansinclusing one side of said member containing a compressible iiuid. andmeans to force a variable quantity of liquid into the housing means tovary its eiectlve volume.

4. Control apparatus comprising means responsive to variations in acondition to produce a pressure proportional to a function oi thecondition. a pair of opposed pressure responsive members connectedtogether and to said means to adjust it.' one of said members beingconnected directly to said means to receive pressure therefrom, meansforming a restricted oriiice connecting the other of said members tosaid means for flow of pressure therebetween, means forming a closedexpansible chamber connected to said members and containing acompressible iluid the volu'me of which is varied as the members move,and adjustable means to vary the eilective volume of the expansiblechamber.

5. Control apparatus comprising means re sponsive to variations in acondition to produce a pressure proportional to a function of thecondition, a pair of opposed pressure responsive members connectedtogether and to said means to adjust it, one oi' said members beingconnected directly to said means to receive pressure therefrom. meansforming a restricted oriilce connecting the other of said members tosaid means for iiowof pressure therebetween, a housing inclosing oneside of one of the members to form a closed chamber containing acompressible fluid whose volume is varied as the member moves, andadjustable means to vary' the eilective volume of the housing.

6; Control apparatus comprising means responsive to variations in acondition to produce a pressure proportional to a function oi thecondition. a pair of opposed pressure responsive members connectedtogether and to said means to adjust it, one of said members beingconnected K directly to said means to receive pressure therefrom, meansforming a restricted oriiice'connecting the other of said members tosaid means for ilow of pressure therebetween, housings incloeing .oneside oi each of said members to form apair sponsive to variations in acondition to produce a' pressure proportional to a function of thecondition, a pair of opposed pressure responsive memquantity of liquidinto saidl chamber to vary its eective volume'.

2. Control apparatus comprising means responsive to variations in acondition for producing a pressure proportional to.. a function of thecondition, a pressure responsive member responbers connected togetherand to said means to adjust it, one of said members being connecteddirectly to said means to receive pressure therefrom, means forming arestricted orifice connecting the other of said members to said meansfor now of pressure therebetween, housings inclosing one side of each ofsaid members to form a pair of inclsed 'chambers whose volumes vary asthe members move. and adjustable means simultaneeii'ective volumes ofthe chambers.

sive to said pressure to be moved thereby and 'I6 8. Control apparatuscomprising means reportional to a function of the condition, an ex-Apansible bellows connected to the means to adjust vit as the bellowsmoves, means connecting one side of the bellows to the means to receivepressure therefrom, a housing inclosing the other side of the sbellowsand lcontaining a compressible fluid, and means for supplying a variablequantity of liquid to the housing to vary its effective volume.

10. Control apparatus comprising means responsive to a condition toproduce a pressure proportional to a function of the condition, a pairof alined expansible bellows, means connecting the bellows to movetogether and to thel means to adjust it, connections from the means toone side of each bellows to conduct pressure thereto,

means forming a restriction in one of the connections, housingsinclosing the other sides of the bellows to form closed chambers, andadjustable means simultaneously to vary the volumes of the chambers. 11.Control apparatus comprising means responsive to a condition to producea pressure proportional to `a function of the condition, a pair ofalined expansible bellows, means connecting the bellows to move'togetherand to the means to adjust it, connections from the means to one side ofeach bellows to conduct pressure thereto, means forming a restriction inone of the connections, housings inclosing the-other sides of Vthebellows to form closed cham-bers, and means simultaneously to supplyliquid to the housings to vary the eiective volume of the chambers.

12. Control apparatus comprising means responsive to a condition toproduce a pressure proportional to a function of the condition, a pairof alined expansible bellows, means connecting the bellows to movetogether and to the means to adjust it, connections from the means toone side of each bellows to conduct pressure thereto, means forming arestriction in one of the connections, housings inclosing the othersides of the bellows to form 4closed chambers containing a compressiblefluid, a pair of liquid iilled expansible chambers communicating withthe housings respectively, and meanssimultaneously to adjust the volumesof the expansible chambers.

13. Control apparatus comprising means responsive to a condition toproduce a pressure proportional to a functionY of the condition, a pairof alined expansible Ibellows, means connecting the bellows to movetogether and to the means to adjust it, connections from the means toone side of each bellows to conduct pressure thereto, means forming arestriction in one of the connections, housings inclosing the othersides of the bellows to form closed chambers containing a compressibleiluid, a pair of housings connected to the first named housingsrespectively and adapted to contain liquid, a pair of expansible bellowssealed in the last named housings respectively, and means forsimultaneously moving the last named bellows.

14. Control apparatus comprising means responsive to a condition toproduce a pressure proportional to a function of the condition; a pairof alined double walled bellows mounted with their adjacent ends'flxed.a rod connecting the outer ends of the bellows, means connecting the rodto said means to adjust it as the bellows move, conadjustable means tovary the volumes of the housings.

JEROME B. McMAHON,

